Wear Tolerant Hydraulic / Pneumatic Piston Position Sensing Using Optical Sensors

ABSTRACT

The present invention relates to using a self calibrating and recalibrating  230, 925  optical sensors piston rod displacement. Self calibration enables field calibration of uncalibrated  230, 925  optical sensors. During operation, recalibration enables detecting and correcting for wear and damage of the  200  piston rod and/or  230, 925  optical sensors.  210  Calibration positions on the surface of the  200  piston rod are imaged by  230  optical sensors using laser or darkfield lenses designed for optical computer mice. Natural surface patterns can be used in locations where  210  calibration positions are required, which reduces or eliminates the need for marked  210  calibration positions. Marked  210  calibration positions are spatially unique encoded sequences used to determine the piston rod absolute position. Storing only the significant features of  210  calibration positions saves significant memory. The reduced memory requirements of each  210  calibration position enables the use of closely spaced or continuous  210  calibration positions. Multiple  210  calibration position features and multiple  230, 925  optical sensors together collectively provide immunity to localized  208  surface damage. Proximity sensors,  925  time of flight sensors and  031  cumulative relative displacement are used to estimate the  200  piston rod absolute displacement and reduce the number of spatially unique  210  calibration positions needed to compare in order to determine the piston rod absolute displacement.

BACKGROUND OF THE INVENTION—OBJECTS AND ADVANTAGES

This invention relates to self calibrating and recalibrating an optical sensor to measure piston rod displacement, thereby enabling initial field calibration and recalibration to correct for wear and damage, and proximity sensors, time of flight sensors, cumulative relative displacement are used to estimate the piston rod absolute displacement and reduce the number of spatially unique calibration positions needed to compare in order to determine the piston rod absolute displacement, thereby reducing memory storage and computational resources required, which enable closely spaced or continuous calibration positions, and the use of naturally occurring speckle patterns as calibration positions reduce the need to use marked encoded sequences as calibration positions.

DESCRIPTION OF PRIOR ART

Piston position sensors (for example, U.S. Pat. No. 9,027,460 B2) that measure the position by series electrical resonates are not easy to implement in practice. Oil conductivity is variable with respect to temperature and pressure. Furthermore, the oil conductivity vs temperature and pressure relationship needs to be re-characterized as the oil ages.

Optical motion sensors (for example, U.S. Pat. No. 8,525,777 B2, U.S. Pat. No. 9,086,738 B2, U.S. Pat. No. 9,342,164 B2, U.S. Pat. No. 7,737,947 B2, U.S. Pat. No. 8,692,880 B2) measures the relative movement of the surface, but are unable to determine the absolute position with respect to the surface.

Optical position sensors (for example, U.S. Pat. No. 8,482,607 B2) are able to determine the absolute position at calibration positions. They do not include an efficient means of storing calibration position images. As result, only a few calibration position images can be stored with the result that estimated absolute position error can grow significantly until corrected at calibration positions.

Optical position sensors (for example, EP patent no. EP2769104 B1) rely on an optically detected code pattern and utilizes light pipes. Etching or otherwise adding these optically detectable code patterns increase the manufacturing cost significantly.

Optical position sensors (for example, U.S. Pat. No. 9,134,116 B2) utilize multiple lasers and/or sensors to provide greater coverage of the curved piston surface than is possible with a single laser and sensor, but are unable to determine the absolute position with respect to the surface.

Optical position sensors (for example, EP patent no. EP2775268 A1) utilize coherent or nearly coherent light to gather speckle interference image for each position. The position between the stored speckle interference images is completely unknown. Without image compression and/or significant point identification, the memory size required to store a large enough number of points to be useful is impractically large.

Optical alignment sensors (for example, CN patent no CN2015/075823) align images utilizing image significant features. However, the images significant features and absolute position is not stored. As result, it is not possible to determine the absolute position.

Optical feature matching is used (for example, U.S. Pat. No. 9,449,238 B2) to improve image correlation in adverse conditions which impact the appearance of images. However the means of collecting images is not provided and is restricted to well defined regular images.

Optical surface movement sensors use light limited to short wavelength (for example, U.S. Pat. No. 8,847,888 B2) to decrease light surface penetration and increase light surface reflection. However reduced light penetration offers no advantage for metal piston rods most commonly used. A combination of narrow band red and blue light is more suitable for penetrating an oil film which may be present and reach the very optically dense metal.

Optical surface movement sensors (for example, U.S. Pat. No. 7,728,816 B2, U.S. Pat. No. 9,052,759 B2) adjust measurement resolution along X and Y axis according to the estimated velocity along the axis. However a means of collecting and storing images is not provided.

Hollow piston rods containing magnetic, microwave and optical sensors within are well established in the field. However it is not practical or cost effective to gun drill or forge long or small diameter piston rods. Optical and radio time of flight sensors require calibration and re-calibration when the optical characteristics change. And low cost external time of flight sensors are vulnerable to objects obscuring the optical path. As a result, optical time of flight sensor used alone to determine the absolute piston rod displacement suffer from low reliability.

SUMMARY OF THE INVENTION

The present invention is using a self calibrating and recalibrating optical sensor to measure piston rod displacement. Self calibration enables field calibration of an uncalibrated optical sensor. During operation, recalibration enables detecting and correcting for wear and damage of the piston rod and/or optical sensors. Natural speckle patterns can be used in locations where calibration positions are required, which reduces or eliminates the need for marked calibration positions. Marked calibration positions are spatially unique encoded sequences used to determine the piston rod absolute position. Storing only the significant features of calibration positions saves significant memory. The reduced memory requirements of each calibration position enables closely spaced or continuous calibration positions. Multiple calibration position features and multiple optical sensors together collectively provide immunity to localized damage. Proximity sensors, time of flight sensors and cumulative relative displacement are used to estimate the piston rod absolute displacement and reduce the number of spatially unique calibration positions needed to compare in order to determine the piston rod absolute displacement.

The optical sensors used to determine the absolute displacement of a hydraulic or pneumatic piston rod relative to its cylinder are calibrated at calibration positions and the absolute displacement is estimated by means of the cumulative of measured relative displacement from said absolute displacement. The steps to estimate the absolute displacement are as follows: Capture images of the piston surface by a CMOS or CCD image sensor using low cost laser or darkfield lens designed for optical computer mice. Arrangements of points that contrast with adjacent surroundings are selected from the captured images. These selected arrangements of significant points are mapped to their corresponding absolute piston rod positions and stored as calibration positions. These significant points which identify a calibration absolute piston rod position is an arrangement of known calibration points. The selected arrangement of points from the current image is aligned with the arrangement of known calibration points of a calibration position.

DRAWINGS—FIGURES

The advantages of this invention may be better understood by reading the following description as well as the accompanying drawings, where numerals indicates the structural elements and features in various figures. The drawings are not necessarily to scale, and they demonstrate the principles of the invention.

FIG. 1 is a flow diagram of the position identification sensing apparatus during operation;

FIG. 2 is a flow diagram of the position identification sensing apparatus during calibration initialization;

FIG. 3 is a flow diagram of calibration storage procedure 036 and 100, 102, 104 calibration database storage;

FIG. 4 is a flow diagram of speckle feature pattern 026/027 correlation with current image significant features 014 during normal operation using FFT-CC;

FIG. 5 is a flow diagram of speckle feature pattern 026/027 correlation with current image significant features 014 during calibration operation using FFT-CC and IC-GN;

FIG. 6 is a flow diagram of the overall operation;

FIG. 7 is a side view diagram of a single laser position identification sensing apparatus;

FIG. 8 is a cross section of a laser speckle pattern image sensing apparatus taken along cutting plain A---A of FIG. 24 illustrating the optical effects of round 200 part under observation;

FIG. 9 is a diagram of spatially additive darkfield;

FIG. 10 is a diagram illustrating the end view of multiple compound speckle pattern image sensing apparatus;

FIG. 11 is a diagram illustrating the top view of a compound speckle pattern image sensing apparatus with the 208 surface of the 200 part under observation below;

FIG. 12 is a diagram illustrating the end view of a compound speckle pattern image sensing apparatus with multiple laser LED taken along cutting plane B-B of FIG. 14;

FIG. 13 is a diagram illustrating the end view of a compound speckle pattern image sensing apparatus with multiple speckle image collectors taken along cutting plane B-B of FIG. 14;

FIG. 14 is a diagram illustrating the bottom view of a compound speckle pattern image sensing apparatus;

FIG. 15 is a graph of the position error bias vs the speckle/pixel size for multiple speckle features sizes;

FIG. 16 illustrates constructing a continuous map of calibration position on the 208 surface of the 200 part under observation;

FIG. 17 illustrates re-selection of calibration position on the 208 surface of the 200 part under observation;

FIG. 18 illustrates the speckle correlation algorithm;

FIG. 19 illustrates abutting non-unique 210 calibration speckle images;

FIG. 20 illustrates non-unique 210 calibration speckle images spaced on 208 surface of the 200 part under observation;

FIG. 21 illustrates 004 frame captures obtained during calibration mapping to 210 calibration speckle image frames;

FIG. 22 illustrates mapping 210 calibration speckle images to 004 frame captures obtained during normal operation;

FIG. 23 is a cross section view of a hydraulic cylinder with an attached photo image sensor taken along cutting plane A-A of FIG. 24;

FIG. 24 is an isometric view of hydraulic cylinder with an attached photo image sensor;

FIG. 25 is a side view of a 200 part under observation with 215 1D calibration patterns at three positions;

FIG. 26 is a side view of a 200 part under observation with spaced 216 2D calibration patterns;

DRAWINGS—REFERENCE NUMERALS

-   001 speckle image -   004 image uniform scale correction -   005 hold until update -   006 convolve with Gabor wavelets -   008 Gabor group selector -   009 position group selector -   010 estimated absolute position for group selection -   012 SURF/SIFT descriptor selector -   014 current speckle image significant features which may also be     known as points of interest -   015 delay until next image capture -   016 finding scale space -   018 feature descriptor -   020 candidate matching SIFT/SURF feature descriptor -   024 speckle pattern selector -   026 speckle feature pattern correlated displacement between 210     calibration position significant features and current image     significant features 014 -   027 speckle feature pattern correlation between previous image     significant features 014 and current image significant features 014 -   030 increment successful match count -   031 cumulative relative speckle displacement from most recent known     position -   032 test condition, is absolute position known -   033 estimated absolute position -   034 new SURF/SIFT descriptor for the known location, new speckle     significant points -   036 calibration storage procedure -   038 relative speckle displacement -   039 unsuccessful relative displacement count -   040 calculated relative speckle 210 calibration position -   041 absolute position from a 918, 919 piston stroke limit sensor, or     from one or more sub-component of a compound position identification     sensing apparatus, or relative position to a part or complete 210     calibration speckle feature with the 209 full speckle view -   042 absolute position from the position sensing algorithm described     in FIG. 1 -   100 database of Gabor wavelets for grouping SURF/SIFT feature     descriptors -   102 database of SURF/SIFT feature descriptors grouped by Gabor     wavelet and by position -   104 database of 210 calibration significant point speckle patterns     indexed by SURF/SIFT feature descriptor -   105 calibration data for 925 time of flight sensors -   110 red laser surface speckle area -   112 blue laser surface speckle area -   114 green laser surface speckle area -   116 darkfield 208 surface area -   120 red laser -   121 red LED -   122 blue laser -   124 green laser -   130 optional source lenses -   135 collector lenses -   200 cylindrical or flat part under observation such as a piston rod -   202 CMOS or CCD image sensor -   208 surface of 200 part under observation -   209 full speckle view -   210 calibration speckle image position of speckle feature area     described by Gabor wavelets, SURF/SIFT feature descriptors and     corresponding significant point speckle pattern -   212 pixels are periodically connected to form 001 speckle image     groupings -   215 spaced binary sequence 1D calibration pattern -   216 spaced binary sequence 2D calibration pattern -   230 optical displacement sensor assembly -   231 microprocessor, FPGA and/or ASIC -   233 non-volatile memory -   234 volatile memory -   242 calibration speckle image features caused by wear -   300 flat part reference plain -   400 mean normalized calibration speckle image -   401 mean normalized current speckle image -   405 Fourier transform of mean normalized calibration speckle image -   406 Fourier transform of mean normalized current speckle image -   410 Inverse Fourier transform of Fourier transform product -   415 FFT-CC x and y displacement at the maximum 410 Inverse Fourier     transform of the Fourier transform 405×406 product, which is a low     resolution 026 speckle feature pattern correlated displacement     between 210 calibration position significant features and current     image significant features 014 -   420 warped arrangement of known calibration points -   421 warped current image significant pattern features with delta     deformation displacement -   425 least squares calculation of delta deformation displacement -   430 delta deformation displacement convergence conditions -   440 IC-GN sub-pixel delta displacement, which is a high resolution     026 speckle feature pattern correlated displacement between 210     calibration position significant features and current image     significant features 014 -   800 start state -   804 initialization, self check and communication state -   820 complete calibration image, including compound calibration image -   825 not surrounded by sufficient 210 calibration points or at end     limits -   832 operation state described in FIG. 1, FIG. 2, and FIG. 3 -   836 simultaneous calculation of precise location described in FIG. 5 -   901 hydraulic cylinder barrel -   902 piston -   903 time of flight piston reflector also known as optical distance     reflector -   904 base stop -   905 head stop -   906 seal in cylinder -   907 hydraulic cylinder head chamber -   908 hydraulic cylinder base chamber -   910 sensing apparatus housing -   912 seals for sensing apparatus -   918 base contact pressure sensor, stroke limit sensor -   919 head contact pressure sensor, stroke limit sensor -   925 time of flight sensor also known as optical distance sensors -   930 sensor pcb board

DETAILED DESCRIPTION

In the following, the described speckle images are either true speckle images caused by coherent laser light interface or facsimile speckle images caused by darkfield surface diffraction. Both speckle images may be additively constructed by overlapping spatial areas as shown in FIG. 9, FIG. 10, FIG. 11, FIG. 12 and FIG. 13.

FIG. 7 is a side view diagram of a single laser position identification sensing apparatus. The coherent light of the 120, 122 or 124 laser passes through a 130 optional source lens illuminating an 110, 112 or 114 speckle area on the 208 surface of the 200 part under observation. The 130 optional source lens refract/bend the narrow laser beam to illuminate a larger area 208 surface of the 200 part under observation. According to Huygens-Fresnel principle, every refracting surface point can be regarded as source for a new wavelet. The wavelets propagate freely without a lens toward the observation plane where they interfere, which result in locally distributed occurrences of constructive and destructive interference. Speckles can be observed from metallic surfaces and show high contrast which makes artificial markers typically unnecessary. The average in-plane speckle d size observed by the 202 CMOS or CCD image sensor is given by

${d = {1.2\frac{\lambda \; u}{D}}},$

where λ is the light wavelength, u is the distance between the 202 CMOS or CCD image sensor and the 208 surface of the 200 part under observation, D is the diameter of illumination on the 208 surface of the 200 part under observation. A 004 image uniform scaling correction step can be used to compensate for the significant difference in u distance across the 202 CMOS or CCD image sensor, between the 202 CMOS or CCD image sensor and the 208 surface of the 200 part under observation.

FIG. 1 refers to the control logic of the position identification sensing apparatus. The data flow and processing steps illustrated in FIG. 1 are as follows. The 001 speckle image is captured by a 202 CMOS or CCD image sensor of single or compound pattern image sensing apparatus. 004 Image uniform scale correction can be applied to correct non-uniform average speckle d size caused by the curved 200 piston rod 208 surface. In the case of a laser pattern image sensor, the non-uniform average speckle size d is caused by varying u distance between the 202 CMOS or CCD image sensor and the 208 surface of the 200 part under observation. The uniform scaled 001 speckle image processed by the 004 image uniform scale correction is 006 convolved with Gabor wavelets retrieved from the 100 database of Gabor wavelets. The 010 estimated absolute position is used to provide 009 position group selection of the SURF/SIFT feature descriptors. The 008 Gabor group selector is used in combination with the 009 position group selector as input to 012 SURF/SIFT descriptor selector. The 012 SURF/SIFT descriptor selector selects ranking groups of candidate matching SIFT/SURF feature descriptors. The result is a reduced number of 020 candidate SURF/SIFT feature descriptors from the 102 database of SIFT/SURF feature descriptors, grouped by Gabor wavelet and by position, that need to be considered.

Databases of 100 Gabor wavelets, 102 SURF/SIFT feature descriptors, and 104 significant point speckle patterns are stored in 233 read/writable non-volatile memory. The control logic is executed on a 231 microprocessor, FPGA and/or ASIC, with temporary execution results preferable stored in 234 volatile memory. Error correcting encoding and redundancy can be used to provide for reliable long term storage and error free control logic execution and data processing.

Continuing the data flow and processing steps illustrated in FIG. 1, the SIFT/SURF algorithm is applied as follows. 014 Significant features of the uniform scaled 001 speckle image are selected in parallel with 006 convolving the speckle image with Gabor wavelets. The SURF algorithm uses a blob detector based on the Hessian matrix to find the points of interest. The next step is to find the 016 scale space from the previously selected significant points. The resulting 018 feature descriptor is matched against 020 candidate matching SIFT/SURF feature descriptors retrieved from the 102 database. If a match occurs, the 024 speckle pattern selector retrieves a 210 calibration image speckle pattern of significant features from the 104 database of significant point speckle pattern features indexed by SURF/SIFT feature descriptors. The end result is the significant features of the current 001 speckle image being 026 correlated with the 210 calibration image speckle feature patterns retrieved from the 104 database.

The data flow and processing steps of the apparatus illustrated in FIG. 1 continue with the 014 speckle image significant feature correlation. The 014 significant features of the current 001 speckle image and the 014 significant features of the previous 001 speckle image are 027 correlated to find the 038 relative speckle displacement. The 014 significant features of the previous 001 are the 014 significant features of the current 001 speckle image 015 delayed until the next image capture. The current and previous 001 speckle images are designed to overlap and will be correlated during normal operation. When the current 001 speckle image and the previous 001 speckle image are found to be not correlated by the 027 correlation operation, the apparatus increments the 039 unsuccessful relative displacement count. High 039 unsuccessful relative displacement count indicates that either 202 CMOS or CCD image sensor is unable to reliably resolve the 208 surface image. Or the current and previous 001 speckle images do not overlap which is perhaps caused by the 200 part under observation moving at an extremely high speed.

The data flow and processing steps illustrated in FIG. 1 describing detection of calibration positions are as follows. The previously selected 210 calibration position's arrangement of significant speckle points are correlated with current image significant points to find the absolute position of the 200 part under observation with respect to the matching 210 calibration position. The components of 210 calibration positions are stored in calibration point databases 100, 102, 104. The 026 speckle feature pattern correlation between 210 calibration position significant features and current image significant features 014 is determined as follows. Please see FIG. 4 for the details of the correlation process. The 210 calibration image speckle feature pattern is correlated with the uniform scaled 001 speckle image using the fast less precise FFT-CC “Fast Fourier Transform Cross Correlation”, shown in FIG. 4. The 210 calibration speckle image at the calibration position is normalized to create a 400 mean normalized calibration speckle image. Then create the 405 Fourier transform of the mean normalized calibration speckle image. The 014 current speckle image significant features are normalized to create a 401 mean normalized current speckle image. Then create the 406 Fourier transform of the mean normalized current speckle image. Combine 405 and 406 Fourier transforms to create the 410 Inverse Fourier transform of the Fourier transform 405×406 product. As shown in FIG. 18, the 415 x, y displacement of the 001 speckle image from the 210 calibration image speckle position within the same 209 full speckle view is found at the maximum 410 Inverse Fourier transform of the Fourier transform 405×406 product.

The data flow and processing steps illustrated in FIG. 1 are further described below. When there is 026 speckle feature pattern correlation between the 210 calibration position significant features and the 014 current image significant features, the correlation is used to obtain the 040 calculated relative speckle 210 calibration position within the 209 full speckle view. When the FFT-CC algorithm is used to obtain the 040 calculated relative position within the 209 full speckle view, it provides the 415 x, y displacement of the 001 speckle image from the 210 calibration speckle image position. If the IC-GN algorithm illustrated in FIG. 5 is used to obtain the 040 calculated relative position within the 209 full speckle view, it provides the high accuracy 440 IC-GN sub-pixel delta displacement of the 001 speckle image from the 210 calibration speckle image position. And as a result the 210 calibration speckle image position on the 208 surface of the 200 part under observation is known relative to the 202 CMOS or CCD image sensor. Whenever a successful correlation match occurs, the 030 successful match count of the 210 calibration speckle image is incremented.

The data flow and processing steps illustrated in FIG. 1 which occur when 210 calibration image speckle positions cannot be matched is as follows. When the highest ranking 020 candidate matching SIFT/SURF feature descriptor fails to be a close match, then another 020 candidate matching SIFT/SURF feature descriptors in the group of SURF/SIFT feature descriptors from 102 database selected by 008 Gabor group and the 009 position group are considered according to their ranking. Similarly, if the 210 calibration position speckle feature pattern corresponding to the candidate SIFT/SURF feature descriptor is not sufficiently close to the 001 speckle image, another candidate SIFT/SURF feature descriptor is selected by 008 Gabor group and the 009 position group. If no more candidates exist, then no match was found. If the 210 calibration speckle image is sufficiently close to the 001 speckle image, then the 040 relative position of the 210 calibration speckle image within the 209 full speckle view is calculated.

The data flow and processing steps illustrated in FIG. 1 and FIG. 2 describing the calibration position update procedure are as follows. The full procedure to update calibration positions is shown in FIG. 1, 2, 6. This procedure initiates when no candidate matching SIFT/SURF feature descriptor is found for the current 001 speckle image within the 209 full speckle view or when no 210 calibration speckle feature is found for the 001 speckle image with the 209 full speckle view. The 041 absolute position can be known by either from one or more position identification sensing apparatus of a compound position identification sensing apparatus such as shown in FIG. 10, or the 041 absolute position is provided by a limit sensor or by the relative position to a part or complete 210 calibration speckle features within the 209 full speckle view. If the 041 absolute position is known, then the Gabor wavelets, SURF/SIFT feature descriptors and speckle features of a 001 speckle image from within the 209 full speckle view can be stored into databases 100, 102 and 104. FIG. 3 is the processing step contained in the 036 calibration storage procedure. In the following description of the 036 calibration storage procedure, reference is made to components tied to, but not contained within the 036 calibration storage procedure. As shown in FIG. 3, if there are 825 not sufficient surrounding 210 calibration speckle image positions or the 200 piston rod is at a displacement end limit, then the 041 absolute position from a limit sensor or from one or more sub-component of a compound position sensor will be used. When a 210 calibration position is required at a location not known from the 041 absolute position from a limit sensor or from one or more sub-component of a compound position sensor, then 836 precise displacement from a previous 041 absolute position is determined using IC-GN algorithm described in FIG. 5. When the 230 optical displacement sensor is at a 041 absolute position, then the 032 test at a known absolute position is true and the absolute displacement can be used to obtain the 014 current speckle image significant features and for 105 calibration data for 925 time of flight sensors. When the 032 test condition indicates a known absolute position, new 210 calibration position data is stored using the 036 calibration storage procedure illustrated in FIG. 3.

If the distance to surrounding calibration positions is too far, one or more 210 calibration speckle images should be selected from within the 209 full speckle view and stored. The maximum distance between calibration positions is determined by the maximum accumulated position error. The accumulated position error is the error between the 033 estimated absolute position and the 041 true absolute position. The 033 estimated absolute position is calculated by adding the cumulative relative displacement to the 041 true absolute position of the last reliable 210 calibration speckle image. The selected 210 calibration speckle image is indexed by Gabor wavelets and relative position to surround 210 calibration speckle images. The corresponding SURF/SIFT feature descriptor of the 210 calibration speckle image is stored into 102 database of SURF/SIFT feature descriptors. And the significant point patterns of the 210 calibration speckle image is indexed by its SURF/SIFT feature descriptor and stored into 104 database of significant point speckle patterns.

210 Calibration speckle feature patterns with high successful match counts are 210 calibration speckle images with stable significant speckle pattern features. When 210 calibration speckle feature patterns change as result of surface wear or sudden surface damage, the 030 increment successful match count no longer increases. Calibration position speckle pattern features which no longer 030 increment their successful match count and are sufficiently close to other calibration position speckle pattern features may be replaced when 233 non-volatile memory is needed to store new 210 calibration speckle feature positions. Calibration maybe required when a sufficient number of calibration position speckle pattern features no longer 030 increment their successful match count and are not sufficiently close to other 210 calibration speckle feature positions.

FIG. 2 refers to the calibration initialization control logic of the position identification sensing apparatus. The 001 speckle image is captured by a 202 CMOS or CCD image sensor of single or compound pattern image sensing apparatus. An 004 image uniform scale correction can be applied to correct non-uniform average speckle d size. Initially there are no stored 210 calibration speckle image positions and the calibration point databases 100, 102, 104 are empty. The first step in storing new 210 calibration positions is selecting 014 significant features from the uniform scaled 001 speckle image. The 041 absolute position can be provided by a 918, 919 piston stroke limit sensor shown in FIG. 23, or from one or more sub-component of a compound position identification sensing apparatus, or relative position to a part or complete 210 calibration speckle feature with the 209 full speckle view. During the initial calibration process, the 041 absolute position is only made available by a 918, 919 piston stroke limit sensor. If the 032 test condition is false, then the absolute position is unknown. And the location is again examined as shown in FIG. 6, until a 041 absolute position such as a 918, 919 piston stroke limit is provided which enables the 032 test condition to be true and the absolute position is known. When the lack of surrounding stored 210 calibration speckle feature positions is detected, it is necessary to assign new stored 210 calibration speckle feature positions. It is important to accurately assign the position of the new 210 calibration speckle features. During calibration, 027 speckle feature pattern correlation between previous image significant features 014 and current image significant features 014 is measured using the 440 IC-GN Inverse Composition Gauss-Newton sub-pixel delta displacement calculation, which is extremely precise, typically ranging from 0.01 to 0.05 pixel. This is 20 to 200 times more precise than the high speed 415 FFT-CC Fast Fourier Transform Cross Correlation used during normal mode to calculate 415 x and y displacement, which typically ranges from 1 to 2 pixels. When the position identification sensing apparatus is searching for new calibration positions, the position identification sensing apparatus is in calibration mode. As the 202 CMOS or CCD image sensor moves over the 200 cylindrical or flat part under observation, windows of 209 full speckle views are periodically captured. In calibration mode, the movement speed of the 202 CMOS or CCD image sensor moves over the 200 cylindrical or flat part is slowed so that the windows of 209 full speckle views are always over lapping by at least one 210 calibration speckle image position. The IC-GN algorithm also takes many times longer than the FFT-CC algorithm. The movement speed during calibration must be reduced to allow for this longer position processing time.

FIG. 16 illustrates a calibration mode 209 full speckle view window step. The initial step is the upper left of the 209 full speckle view. During the initial window step, four 210 calibration speckle image positions are selected from the four corners of the 209 full speckle view. If a 210 calibration speckle image position is completely enclosed within the overlapping 209 full speckle views, such as the upper left of the second 209 full speckle view window step, it does not need to be saved. The displacement between 209 full speckle views is precisely measured using the 440 IC-GN “Inverse Composition Gauss-Newton”.

The 210 calibration image speckle feature pattern is correlated with the 001 speckle image using the slower precise IC-GN “Inverse Composition Gauss-Newton”, shown in FIG. 5. In FIG. 5, similar to FIG. 4, the 210 calibration speckle image at the calibration position is normalized to create a 400 mean normalized calibration speckle image. The 014 current speckle image significant features are normalized to create a 401 mean normalized current speckle image. The next step is to create the 405 Fourier transform of the mean normalized calibration speckle image. Simultaneously the next step is to create the 406 Fourier Transform of the mean normalized current 001 speckle image. Combine 405 and 406 Fourier transforms to create the 410 Inverse Fourier Transform of the Fourier transform 405×406 product. As shown in FIG. 18, the 415 x, y displacement of the 001 speckle image from the 210 calibration speckle image position is within the same 209 full speckle view. In FIG. 5, the 415 FFT-CC x & y displacement is found at the maximum 410 Inverse Fourier Transform of the Fourier transform 405×406 product. The calculated 415 FFT-CC x & y displacement is the initial guess x & y displacement used in the 440 IC-GN algorithm. The 421 warped current image is calculated as a function of the 401 mean normalized current speckle image and the current deformation. The 420 warped arrangement of known calibration points is calculated as function of the 400 mean normalized calibration speckle image. A 425 least squares calculation of delta deformation displacement is calculated on the combined 400 warped arrangement of known calibration points and 401 mean normalized current speckle image. When the 425 least squares calculation of delta deformation displacement meets the 430 delta deformation displacement conditions, the current 425 least squares calculation of delta deformation is the final 440 IC-GN sub-pixel delta displacement. Otherwise, the current 425 least squares calculation of delta deformation displacement is used to calculate the next 421 warped current image.

FIG. 17 illustrates the bottom right 210 calibration speckle image position from the previous 209 full speckle view deleted and replaced by a 210 calibration speckle image position with a high density of significant features. When the density of significant features is high as shown in FIG. 17, a single 210 calibration speckle image is sufficient to uniquely define a calibration position on the 208 surface of 200 part under observation. When the density of significant features is low as shown in FIG. 18, two or more abutting 210 calibration speckle images are used to uniquely define a calibration position on the 208 surface of 200 part under observation. As the calibration progresses, either a single 210 calibration speckle image sufficient to uniquely define a calibration position or two or more abutting 210 calibration speckle images sufficient uniquely define a calibration position are saved for each successive 209 full speckle view window step. In calibration mode, it is not necessary to systematically sweep over the 200 cylindrical or flat part under observation. The 210 calibration speckle image in each 209 full speckle view window step is retained until there are sufficient 210 calibration speckle image positions in all directions for the 200 cylindrical or flat part under observation. These retained 210 calibration speckle image positions are used as 041 reference absolute positions to measure displacement to 210 calibration speckle image positions along alternate paths. When 210 calibration speckle image positions are surrounded by sufficient 210 calibration speckle image positions in all directions, a single 210 calibration image speckle is sufficient to provide locally unique identification of the calibration position. Also 210 calibration position with higher density of significant features are retained and the previously required abutting 210 calibration speckle images are deleted.

FIG. 6 is a flow diagram describing the overall operation of the position identification sensing apparatus. On power up or reset the position identification sensing apparatus, enters the 800 start state. In 800 start state, the boot code is launched, which may include microcode, firmware and software. From the 800 start state, the position identification sensing apparatus enters the 804 initialization, self check and communication state. In the 804 state, the position identification sensing apparatus prepares to begin its function of identifying the position of 200 cylindrical or flat part under observation with respect to 202 CMOS or CCD image sensor.

The 042 absolute position from the position sensing algorithm and 033 estimate absolute position are the provided outputs used to determine the absolute position. The initial 033 estimated absolute position is obtained from 041 known absolute position from a 918, 919 piston limit extension/retraction sensor or from a calibrated 925 time of flight sensor. If the 925 time of flight sensor is uncalibrated, it can be calibrated using 041 known absolute positions as shown in FIG. 3. The operation procedure described in FIG. 1 is performed on each frame captured 001 speckle image. The 010 estimated absolute position used for group selection greatly reduces the possible 210 calibration position known significant feature sets to be matched against the 014 current speckle image significant feature. Operation during calibration mode depends on 041 known absolute positions from a 918, 919 piston extension/retraction limit sensor or a calibrated 925 time of flight sensor for the 036 calibration storage procedure of new 210 calibration positions. When operating in normal mode, the 042 absolute position is determined by either the 040 calculated relative speckle 210 calibration positions or by the position calculated from the 036 calibration storage procedure. The 042 absolute position calculated from 036 calibration storage procedure is preferentially selected to be the most reliable. The most recent 042 absolute position and the 925 time of flight estimated position are 005 held in volatile memory until updated with newer values. The 033 estimated absolute position is calculated by the combined most recent known position 005 held in volatile memory and the 031 cumulative relative speckle displacement. The 031 cumulative relative speckle displacement is the accumulated 038 relative speckle displacement. An external source of 031 relative speckle displacement can improve and/or verify the net 038 relative speckle displacement estimation.

The 832 operation state shown in FIG. 6 is described in FIGS. 1, 2, 3, 4, and 5. The 032 test condition, is the absolute position corresponds to the known 041 absolute position from a limit sensor, or from one or more sub-component of a compound position identification sensing apparatus, or relative position to a part or complete 210 calibration speckle feature within the 209 full speckle view as shown in FIG. 1 and FIG. 2. If the absolute position has not been identified, then sensing apparatus will continue to apply the 032 test condition to determine if the absolute position is known, as the 202 CMOS or CCD image sensor moves over the 208 surface of 200 part under observation. After the 032 test condition determines the absolution is known and 202 CMOS or CCD image sensor is at a 210 calibration speckle image position, the next step is to check whether this is an incomplete 820 compound calibration image constructed of abutting 210 calibration speckle image positions. If the current 210 calibration speckle image position is an incomplete part of 820 compound calibration image constructed of abutting 210 calibration speckle image positions, then the known absolution position 032 test condition is updated with the found portion of the 820 compound calibration image.

FIG. 7 illustrates the varying speckle size which occurs while observing a round 200 part under observation. Light from the 120 laser is unfocused by the 130 optional source lens to cover the 110 speckle area. The average speckle

$d = {1.2\frac{\lambda \; u}{D}}$

size is correspondingly larger when the u distance between the 202 CMOS or CCD image sensor and the 208 surface of 200 part under observation is larger. A 004 image uniform scaling correction step can be used to compensate for the non-uniform average speckle d size.

FIG. 8 illustrates nonuniform speckle size resulting from a curved 208 surface of 200 part under observation. The u₁ distance between the 202 CMOS or CCD image sensor and the 110 laser speckle surface reflection is greater when the curved 208 surface of 200 part under observation is further away than the u₂ distance to the 300 flat part reference plain.

FIG. 9 is a diagram of spatially added darkfield. The objective is to select 210 calibration speckle images with a sufficiently high density of significant features to uniquely define a calibration position on the 208 surface of 200 part under observation. And the objective is not to measure the topology of the 208 surface of 200 part under observation. A 121 LED light source shines through a 130 optional source lens and illuminates the 208 surface of 200 part under observation. Each 135 collector lens or compound 135 collector lens collects darkfield scattered light from separate or overlapping 116 darkfield areas. Light pipes are able to provide the same function as multiple/compound 135 collector lens. In this implementation, multiple/compound 135 collector lens are preferred over light pipes due to their superior low distortion optical properties. The darkfield scattered light from multiple 116 darkfield areas is additively collected by the 202 CMOS or CCD image sensor. The magnifying power of the 135 collector lenses is chosen so that the facsimile speckle size is greater than 4 pixels×4 pixels. As illustrated in FIG. 8, a curved 208 surface of 200 part under observation reduces the reflected 110 speckle area. Multiple or compound 135 collector lens are ideally arranged along the length of the length of curved 200 part under observation.

FIG. 10 and FIG. 11 illustrate multiple compound speckle pattern image sensing apparatus covering separated areas of the 208 surface of 200 part under observation. FIG. 10 illustrates the end view of multiple compound speckle pattern image sensing apparatus. FIG. 11 illustrates the top view of a compound speckle pattern image sensing apparatus with the 208 surface of the 200 part under observation below. Experimental observation has indicated events that damage the 208 surface of 200 part under observation cause localized damage. Multiple collectively unique 210 calibration speckle images are stored for each 210 calibration position, preventing loss of the 210 calibration position for most common damage events. When some 210 calibration speckle images are damaged, the calibration position is still recognizable providing that there are remaining 210 calibration speckle images which are locally unique. The relative position of the 210 calibration speckle images to other 210 calibration speckle image positions can uniquely resolve the 210 calibration speckle image position from other similar 210 calibration speckle image positions.

When the 209 full speckle view, shown in FIG. 16, 17, 18 is large enough, multiple collectively unique 210 calibration speckle images can be stored for each calibration position within the 209 full speckle view. Compound speckle pattern image sensing apparatus shown in FIG. 10 and FIG. 11 increases the 209 full speckle view area. However when the multiple collectively unique 210 calibration speckle images are in close proximity within a single 209 full speckle view area and 208 surface damaged in a local area could result in damage to multiple 210 calibration speckle images. 210 Calibration positions constructed of collectively unique 210 calibration speckle images from multiple speckle pattern image sensing apparatus are shown in FIG. 16, 17, 18. They are widely separated over the 208 surface of 200 part under observation. The widely separated 210 calibration speckle images are far less effected by events that damage the 208 surface of 200 part under observation. Damage is typically restricted to a sub-component of the multiple speckle pattern image sensing apparatus. The collectively unique 210 calibration speckle images enables instantaneous or rapid detection of changes to 210 calibration speckle images and reliably updating the 210 calibration speckle images.

FIGS. 12 and 13 illustrate compound image sensing apparatus. The relative positions of the 202 CMOS or CCD image sensor and 120 Laser or 121 LED light sources are illustrative and are not an exact cross section of image sensing apparatus shown in FIG. 14. The single 202 CMOS or CCD image sensor illustrate in FIG. 12 is highly suitable for additive darkfield feature collection. 210 calibration positions require that the 208 surface of 200 part under observation is large enough to insure unique speckle patterns. The multiple 202 CMOS or CCD image sensors illustrated in FIG. 13 is suitable for laser speckle patterns or lateral orientation. Large 208 surface areas of 200 part under observation can be created by joining connected 208 surface areas by means of continuous observations as the laser speckle pattern image sensing apparatus passes over the 208 surface of 200 part under observation. This requires low error stitching of the observations together to form surface areas large enough to insure unique speckle patterns at calibration locations. As illustrated in FIG. 3, increasing the 202 CMOS or CCD image sensor size corresponding to a larger 208 surface of 200 part under observation significantly increases distortion caused by non-uniform average speckle size. However large 202 CMOS or CCD image sensors have high complexity and cost. The compound speckle pattern image sensor increases the 208 surface of 200 part under observation by using multiple 202 CMOS or CCD image sensors as shown in FIG. 10. The advantage is the smaller 208 surface of 200 part under observation corresponding to each 202 CMOS or CCD image sensor requires less 004 image uniform scaling. The compound laser speckle pattern image sensor such as illustrated in FIG. 11 can also increase the combined 208 surface of 200 part under observation by using a RGB 202 CMOS or CCD image sensors to combine the separate 110 laser speckle areas or 116 darkfield 208 surface areas.

FIG. 14 is the bottom view of a speckle pattern image sensing apparatus. The essential components of the compound of an image sensing apparatus are the 202 CMOS or CCD image sensor, one or more 120, 122, 124 laser or 121 led light sources, 230 sensor board, 231 microprocessor, FPGA and/or ASIC, 202 CMOS or CCD image sensor, 233 non-volatile memory and 234 volatile memory. Laser light sources produce laser speckle images. While led light sources would be typically used to produce darkfield images. The components 202 CMOS or CCD image sensor, one or more laser 120, 122, 124 coherent light source, 231 microprocessor, FPGA and/or ASIC, 233 non-volatile memory and 234 volatile memory are soldered to and electrically interconnected by the 230 sensor board. The 202 CMOS or CCD image sensor, one or more laser 120, 122, 124 coherent light source may be built as sub-module to facilitate easy correct placement of any 130 optical source lens used. The 231 microprocessor, FPGA and/or ASIC SOC, system on chip including 233 non-volatile memory and 234 volatile memory are required for execution of the control logic. A compound laser speckle pattern image sensing apparatus uses more than one 120 red laser, 122 blue laser, 124 green laser coherent light source and 202 CMOS or CCD image sensor with corresponding pixel red, blue, green colour. A simple non-compound laser speckle pattern image sensing apparatus uses only one 120 red laser, 122 blue laser or 124 green laser coherent light source and a black and white 202 CMOS or CCD image sensor.

FIG. 15 is a graph of the position error bias vs speckle/pixel size. The lines on the graph are the pixel width/feature width which is effectively pixel size/feature size for unity aspect ratios. The graph requires that the pixel array size is larger than the feature size. As result, feature size determines the minimum pixel array size. 210 Calibration positions large enough to ensure unique speckle patterns can be the combined 208 surface of all sub-components of the multiple compound laser speckle pattern image sensing apparatus such as shown in FIGS. 9, 10, 12, and 13.

The bias effect is shown to decrease as the speckle/pixel size increases and thus the Nyquist criteria is obeyed. When the speckle/pixel size is below 2 pixels×2 pixels, the Nyquist criteria, noise obstructs a precise determination of the speckle displacement. And the obstructed precise determination of the speckle displacement prevents 210 calibration positions with stable arrangements of significant points contrasting with adjacent surroundings. When pixel imaging errors and defects of 202 CMOS or CCD image sensor are taken into consideration, it is recommended that the speckle size is greater than 4 pixels×4 pixels along the horizontal and vertical axis of the 202 CMOS or CCD image sensor.

FIG. 17 illustrates a 210 calibration position natural speckle feature on the 208 surface of 200 part under observation. The entire 208 surface of 200 part under observation produces natural speckle patterns. For clarity, FIG. 17 only illustrates the natural speckle features at a 210 calibration position within a 209 full speckle view. The 210 calibration position natural speckle features are described by Gabor wavelets, SURF/SIFT feature descriptors and corresponding significant point speckle pattern. The complete speckle pattern is not stored, as result the reduced 234 volatile memory requirements can enable complete coverage of the 208 surface of 200 part under observation with 210 calibration positions.

FIG. 19 illustrates abutting 210 calibration images positions. Each abutting 210 calibration image has few points of interest and has at least one SURF feature. After 804 initialization, the first detected 210 calibration image during 832 operation is unlikely to be uniquely mapped to an 041 absolute position. The matched 210 calibration image will assist the 009 position group selection of the 020 candidate matching SIFT/SURF feature descriptor. As the 832 operation continues, the relative position of additional matched 210 calibration images uniquely defines the absolute position. Once the 041 absolute position has been determined by the relative position of a collection of 210 calibration images, each subsequent detected 210 calibration image indicates the new absolute position by the relative position of the collection of 210 calibration images. No effort is taken to ensure that any 210 calibration position does uniquely define the absolute position. Every abutting 209 full speckle view contains at least one complete 210 calibration image. With no gaps between the simple 210 calibration image positions, there is no need to estimate the absolute position based on the relative displacement from the last known absolute position. The relative displacement from the previous 210 calibration images reconfirms the absolute position of the current 210 calibration image. The 210 calibration image only needs to be unique within the relative displacement error. Every abutting 209 full speckle view contains at lease one 210 calibration image, so that relative displacement error cannot accumulate between 210 calibration image positions. The 210 calibration image requires very few points of interest and very simple feature to be sufficiently unique. If the current 210 calibration image has been damaged, the current absolute position is known by calculating the precisely relative displacement from surrounding 210 calibration images. Using the current known absolute position a replacement 210 calibration image is selected and stored as previously described by FIG. 3.

FIG. 20 illustrates some randomly separated 210 calibration images positions surrounded by 210 calibration images separated by some distance. Each 210 calibration image has few points of interest and has at least one SURF feature. After 804 initialization, the absolute position is likely completely unknown until a 210 calibration image is matched. Even after a 210 calibration image is matched during 832 operation, it is unlikely to be uniquely mapped to an absolute position. The matched 210 calibration image and relative displacement between surrounding 210 calibration images will assist with the 009 position group selection of the 020 candidate matching SIFT/SURF feature descriptor. As the 832 operation continues, the relative position of additional matched 210 calibration images uniquely defines the absolute position. After the absolute position has been determined, the absolute position is estimated from relative displacement from the absolute positions of the surrounding 210 calibration images. When a 210 calibration image is damaged, it is not detected where expected. Each time a 210 calibration image is not detected near its 033 estimated absolute position, the 030 increment successful match count is not incremented. With insufficient reliable calibration image points, precise relative displacement from surrounding 210 calibration image positions is calculated until a replacement 210 calibration image is stored. When the most recent 210 calibration image position is different from the 210 calibration image position previously used, the new 033 estimated absolute position which is a less precise absolute position is used to statistically verify that the set absolute displacement of the new 210 calibration image position is correct. No effort is taken to ensure that any 210 calibration position uniquely defines the 041 absolute position.

The 041 absolute location of the 210 calibration positions is recorded during calibration mode. The process of mapping frame captured 001 speckle images to 210 calibration position frames is shown in FIG. 21. During calibration mode, the selection of 014 points of interest can be performed on all speckle images or the selection of 014 points of interest can be delayed until new speckle significant points are required for a 034 new SURF/SIFT descriptor for the known location. Once the 041 absolute position is known, the current capture frame can be used as a reference frame. On the first pass of the calibration mode operation, no 210 calibration positions have been recorded and the 925 time of flight sensor has not been calibrated. The known position of the 200 piston rod at full extension and full retraction is used as the initial known 041 absolute positions. These known 041 absolute positions are used to calibrate the 925 time of flight sensor and select a reference frame. In calibration mode, the 208 surface of 200 part under observation is mapped with frames abutting the selected reference frame. As the 230 optical displacement sensor moves over the 208 surface of 200 part under observation, 001 speckle images frames are captured. Many 001 speckle images frames may overlap with each abutting frame mapping the 208 surface of 200 part under observation. If sufficient memory is available, every abutting frame is used to store a 210 calibration image as shown in FIG. 19. When there are no gaps between the calibration positions, the 033 estimated absolute position is the absolute position of the 210 calibration positions. 212 Pixels can be periodically connected to form 001 speckle image comb filter groupings. The individual pixels or pixel groupings are connected to ADC analog digital converters that convert the pixel photo intensity into a binary representation used as the 001 speckle image. The 212 pixel periodically connected to form 001 speckle image comb filter groupings reduces the memory required to store the 210 calibration speckle image significant features and the computation effort required to match the 014 current speckle image significant features with stored 210 calibration speckle image significant features. Darkfield surface diffraction by its nature is concentrated to features and is not uniform over the surface. Many of the pixels of 212 periodically connected 001 speckle image comb filter groups will not simultaneously receive darkfield surface diffraction illumination. Alternate prior art 001 speckle image grouping implementation commonly used is grouping pixels to form 2×2 001 speckle image bins of neighbouring pixels. 2×2 or 4×4 001 speckle image bins of neighbouring pixels reduces the resolvable feature details.

A comb array can alternately be represented as a discrete Fourier transform (DFT). It can be concluded that a 1D comb array is essentially a 1D correlation at a special frequency. The 212 periodically connected 001 speckle image comb filter illustrates a 2D comb array with 4×4 elements per cell. Within each cell the 4×4 elements is illustrated by the lines; dotted, short dash, long dash, solid. The 212 periodically connected 001 speckle image comb filter of 4×4 cell elements is repeated. Each pixel element of the 4×4 cell is connected to the corresponding pixel element of adjacent cells. Alternative implementations may include 2D comb arrays having other than 4×4 pixel elements per cell, 2D comb arrays with sub-arrays or 2D comb arrays with dynamically reconfigurable comb connections to enable the spatial frequency to be dynamically changed.

The resolution of dynamically reconfigurable 2D comb arrays can be modified; by adjusting the resolution of the attached ADC, by reconfiguring the electrical connections of the pixels to the attached ADC, or by varying the combination of ADC binary pixel representations used as the 001 speckle image. The reconfigurable combination of ADC produced binary pixel representations used as the 001 speckle image is the preferred implementation. Equivalently the 001 speckle image can be reconfigurably combined in the 004 image uniform scale correction stage of the algorithm. 212 periodically connected 001 speckle image comb filter has the benefit of hardware enabled pixel correlation.

When there are gaps between the 210 calibration positions as shown in FIG. 20, the 033 estimated absolute position is obtained by measuring relative displacement from the previous 210 calibration position. Small errors in the measured relative displacement accumulate which result in error in the 033 estimated absolute position. The variance and mean is calculated of pixels within the 210 calibration frame from 001 speckle images frames overlapping with the 210 calibration frame. If the variance is uniformly too large, there is pixel misalignment error and the 440 IC-GN sub-pixel delta displacement algorithm is required or more iterations of the 440 IC-GN sub-pixel delta displacement algorithm are required. Points with high variance are not good candidates for 014 current speckle image significant features and should not be used for the 210 calibration image significant points. The 210 calibration speckle image selected significant points can be natural features or etching or laser blacken features. There is no need for precise location control when etching the unique features. Good candidate features are 215 1D binary encoded calibration patterns shown in FIGS. 25 and 216 2D binary encoded calibration patterns shown in FIG. 26. The relative pattern geometry is enough to describe the 215 1D binary encoded calibration and 216 2D binary encoded calibration patterns as sequence, which greatly reduces the memory required to store either 215 1D binary encoded or 216 2D binary encoded calibration patterns. The precise location of each element of the binary encoded patterns is located using the method previously described for storing natural features as 210 calibration positions.

In FIG. 22, 210 calibration positions have been previously recorded in calibration mode described in FIG. 21. These 210 calibration position may have been natural features as shown in FIGS. 16, 17 and 18 or etched 215 1D/216 2D calibration positions. The 033 estimated absolute position is obtained by measuring relative displacement from the previous 210 calibration position and/or the 925 time of flight sensor. The ranging rate of the 925 time of flight sensor and its vulnerability to optical interference are key limitations of 925 time of flight sensors. Low cost 925 time of flight sensor is able to estimate the absolute position which dramatically reduces the time required to locate 210 calibration positions. The 033 estimated absolute position is used by the 009 position group selector as input to 012 SURF/SIFT descriptor selector of the candidate 210 calibration position. With knowledge of the 033 estimated absolute position, a few 014 significant feature points within the 001 speckle image capture frame are sufficient to detect the 210 calibration position and determinate the 041 absolute position.

FIG. 23 shows a side cross-sectional view of an embodiment of a hydraulic cylinder assembly with a 230 optical displacement sensor assembly. The hydraulic cylinder assembly includes a 901 cylinder barrel and a 910 sensing apparatus housing. A 902 piston is arranged within the 901 cylinder barrel for reciprocating motion along an axis in response to hydraulic fluid. The 902 piston partitions the cylinder barrel 901 into two chambers, 907 and 908. The 910 housing is securely mounted on the 901 cylinder barrel.

One end of a 200 piston rod is fixed to the 902 piston and extends along the axis of the movement. The other end of the 200 piston rod extends out of the 910 housing. Either or both the cylinder base and outside end of the 200 piston rod maybe connected directly or indirectly with a machine component.

The 901 cylinder barrel has two openings for the passage of fluid such as oil or water into and out of the chambers 907, 908 for moving the 902 piston. 906 Seals within the 901 cylinder barrel are arranged to lie flush with the surface of the 200 piston rod and thus prevent fluid from leaving the 907 chamber.

The 910 housing encloses a 230 optical displacement sensor, which is used to determine the instantaneous position of the piston rod 200. The 912 seals within the 910 housing are arranged to clean the surface of the 200 piston rod and thus prevent fluid or dirt from contaminating the 230 optical displacement sensor. The 910 housing provides protection for the 230 optical displacement sensor assembly from the environment and permits easy replacement of the sensing unit. The 230 optical displacement sensor is mounted in the 910 housing within proximity of the piston rod's surface to permit reading of the movement of the 200 piston rod.

The 919 head contact pressure sensor is mounted at the 905 head stop of the 901 cylinder barrel. The 918 base contact pressure sensor is mounted at the 904 base stop of the cylinder barrel 901. Together these two contact sensors provide a two-bit digital signal to indicate whether the 902 piston reaches the 905 head stop or the 904 base stop, or neither. Correspondingly when the 902 piston reaches either the head 905 or base stop 904, the absolute displacement information in storage is adjusted and updated. The 925 time of flight sensors are mounted on the 910 housing and directed towards the 903 time of flight reflector attached to the 200 piston rod. The 925 time of flight sensors are calibrated at the 905 head stop and/or the 904 base stop. The 925 time of flight sensors estimate the 200 piston rod extension which is improved with the 230 optical displacement sensor.

In operation, fluid forced into or removed from the 907, 908 chambers at time-varying pressures causes the piston 902 and thus the 200 piston rod to slide back and forth relative to the 230 optical displacement sensor. The 230 optical displacement sensor reads the relative displacement of the 200 piston rod and produces a corresponding digital signal. The 231 microprocessor, FPGA and/or ASIC on the sensor board 930 calculates the absolute displacement of the 200 piston rod by matching the calibration pattern and using the relative displacement. The obtained absolute displacement indicates the actual position of the 200 piston rod and 902 piston.

FIG. 24 is an isometric view of hydraulic cylinder with an attached photo image sensor and shows the cutting line A-A used to obtain the cross section shown in FIG. 23.

FIG. 25 is a diagrammatic view of 200 part under observation with 215 1D binary encoded calibration patterns. The number of calibration patterns is not confined to three. The number and placement of calibration patterns is determined by application requirements. Unique calibration patterns make it possible to determine which is the current calibration position based on its calibration pattern. The absolute location of the 215 1D binary encoded calibration patterns is determined during calibration mode, which enables the use of lower cost laser etching of the 215 1D binary encoded calibration patterns.

FIG. 26 is a diagrammatic view of 200 part under observation with 216 2D binary encoded calibration patterns. The number and placement of calibration patterns is determined by application requirements. Unique calibration patterns make it possible to determine which is the current calibration position based on its calibration pattern. The absolute location of the 216 2D binary encoded calibration patterns is determined during calibration mode, which enables the use of lower cost laser etching of the 216 2D binary encoded calibration patterns. The reduced etching needed for the widely spaced 216 2D binary encoded calibration patterns is able to further reduce manufacturing costs. 

What is claimed is:
 1. An optical apparatus for measuring absolute mechanical displacement of actuators, joints, or other mechanical apparatus that contain mechanical parts that move with respect to each other, comprising: a) an 230 optical means of capturing 001 images directed at the 208 surface of a 200 moving part of said mechanical apparatus under observation that moves with respect to said 230 optical means of capturing 001 images, such that said 230 optical means of capturing 001 images is mounted onto another part of said mechanical apparatus, b) a means of selecting 014 points that contrast with adjacent surroundings from said 001 images, c) a plurality of 210 calibration positions, such that at each said 210 calibration position, there is an arrangement of known calibration points that contrast with adjacent surroundings on said 208 surface, and d) a means of 026 detecting alignment of said 200 moving part with said 230 optical means of capturing 001 images at said 210 calibration position by matching said 014 points that contrast with adjacent surroundings with said known calibration points that contrast with adjacent surroundings, such that the absolute position of said 200 moving part with respect to said 230 optical means of capturing 001 images is said known absolute position, whereby said known absolute position of said 200 moving part with respect to said 230 optical means of capturing 001 images is corrected at said 210 calibration positions, and whereby said 210 calibration positions do not require markings on said 208 surface of said 200 moving part of said mechanical apparatus under observation.
 2. The optical apparatus of claim 1, further including: a) one or more means of detecting the absence of sufficient said 210 calibration positions for alignment of said 200 moving part with said 230 optical means of capturing 001 images, b) one or more means of obtaining the absolute displacement of said 200 moving part with respect to said 230 optical means of capturing 001 images, and c) a means of storing said 210 calibration position, such that at each said 210 calibration position, said absolute displacement of said 200 moving part with respect to said 230 optical means of capturing 001 images is known and such that at each said 210 calibration position, said calibration points that contrast with adjacent surroundings are known, whereby said 210 calibration positions for alignment of said 200 moving part over complete said 208 surface of said 200 moving part, and whereby said 210 calibration positions are stored to replace any obscure said 210 calibration positions.
 3. The optical apparatus of claim 1, further including: a) a means of obtaining a measured absolute position on said 208 surface of said 200 moving part with respect to said 230 optical means of capturing 001 images, b) a means of identifying said 210 calibration positions where said 026 detected alignment is detected near said known absolute position of said 210 calibration positions and said measured absolute position of said 200 moving part does not match said known absolute position of said 210 calibration position, such that said known absolute positions of said identified 210 calibration positions can be updated, and c) a means of identifying said 210 calibration positions where said 026 detected alignment is not detected near said known absolute position of said 210 calibration positions, such that said identified 210 calibration positions can be deleted, whereby said means of measuring absolute position is able to verify said known absolute position of said 210 calibration positions, whereby said means of measuring absolute position is able to improve the accuracy of said known absolute position of said 210 calibration positions, whereby said means of measuring absolute position is able to identify and delete said 210 calibration positions which are no longer detectable, and whereby said optical apparatus is able to release memory used by said 210 calibration positions which are no longer detectable.
 4. The optical apparatus of claim 1, further including: a) one or more means of measuring relative displacement of said 200 moving part from the previous position of said 200 moving part with respect to said 230 optical means of capturing 001 images, and b) a means of obtaining a measured absolute displacement from the cumulative said measured relative displacement and from said known absolute positions of said 210 calibration positions, whereby said measured absolute displacement is estimated between said known absolute positions of said 210 calibration positions, and whereby said mechanical apparatus cost is reduced through the reduced number of required said 210 calibration positions.
 5. The optical apparatus of claim 1, wherein said known calibration points that contrast with adjacent surroundings are selected to be a globally unique 018 feature, such that said globally unique 018 feature is unique among all said known calibration points, whereby the global absolute position is known by the relative positions of said globally unique 018 features.
 6. The optical apparatus of claim 1, further including: a) a means of obtaining a measured absolute position of said 200 moving part with respect to said 230 optical means of capturing 001 images, and b) said known calibration points that contrast with adjacent surroundings selected to be a locally unique 018 feature, such that said locally unique 018 feature is unique within the measurement error of said measured absolute position, whereby selected said locally unique 018 features can be very simple and only need to be unique within the relatively small area defined by said measurement error of said measured absolute position, and whereby said locally unique 018 features are simple requiring less 233 non-volatile memory, thus enabling more said locally unique 018 features to be stored.
 7. The optical apparatus of claim 1, wherein said 210 calibration positions are adjacent, such that the absolute position is obtained from one or more said 210 calibration positions, and whereby said absolute position error does not occur between said 210 calibration positions.
 8. The optical apparatus of claim 1, wherein the relative position of said arrangements of known calibration points of said 210 calibration positions uniquely defines the absolute position, such that said arrangements of known calibration points of said 210 calibration positions are locally unique as required to determine said relative position of said 210 calibration positions, whereby said relative position of additional said 210 calibration positions provides detection and correction of errors caused by change in one or more said arrangements of known calibration points, whereby the locally unique said arrangement of known calibration points are less complex, requiring less 233 non-volatile memory, thus enabling more said locally unique 018 features to be stored.
 9. The optical apparatus of claim 1, wherein said 210 calibration positions, are marks created on said 208 surface of said 200 moving part, such that said 210 calibration positions are encoded sequences, such that said 210 calibration positions with one dimensional encoded sequences have their said known absolute position defined by one dimension, whereby creating marks on said 208 surface of said 200 moving part ensures that said 210 calibration positions with said known calibration points that contrast with adjacent surroundings are said encoded sequence requiring significantly less 233 non-volatile memory, whereby creating marks on said 208 surface of said 200 moving part ensures that said 210 calibration positions with said known calibration points are located sufficiently close to ensure an acceptable measurement error, and whereby creating marks on said 208 surface of said 200 moving part ensures that said 210 calibration positions with said known calibration points can be sparsely located to minimize manufacturing costs.
 10. The optical apparatus of claim 1, wherein said 210 calibration positions are selected natural calibration points that contrast with adjacent surroundings, whereby a manufacturing process of creating marks on said 208 surface of said 200 moving part is not required, which reduces manufacturing cost.
 11. The optical apparatus of claim 1, wherein said means of 026 detecting alignment of said 200 moving part further includes: a) one or more 903 optical distance reflector moving together with said 200 moving part of said mechanical apparatus under observation, and b) one or more 925 optical distance sensor moving together with said 230 optical means of capturing 001 images, such that said one or more 925 optical distance sensors measures the distance to said one or more 903 optical distance reflectors, whereby said 925 optical distance sensors reduces the number of candidate said 210 calibration positions to be searched for a match, and whereby said 925 optical distance sensors assist said means of 026 detecting alignment of said 014 points with said known calibration points and reduces computational cost.
 12. An optical method of measuring absolute mechanical displacement of actuators, joints, or other mechanical apparatus that contain mechanical parts that move with respect to each other, comprising the steps of: a) measuring relative displacement of a 200 moving part of said mechanical apparatus by 230 optically capturing images of said 200 moving part which is moving with respect to means of said 230 optically capturing images, such that said means of said 230 optically capturing images is mounted onto another part of said mechanical apparatus, b) obtaining known absolute displacement of said 200 moving part at 210 calibration positions, and c) estimating absolute displacement of said 200 moving part by means of the cumulative said measured relative displacement from obtained said known absolute displacement of said 210 calibration positions, whereby absolute displacement of said 200 moving part that moves with respect to means of said 230 optically capturing images is corrected at 210 calibration positions.
 13. The optical method of claim 12, wherein the method of obtaining said known absolute displacement of said 200 moving part, comprises the steps of: a) capturing 001 images of the 208 surface of said 200 moving part by means of said 230 optically capturing images, b) selecting arrangements of 014 points from said 001 captured images that contrast with adjacent surroundings, c) storing said selected arrangements of 014 points at said 210 calibration positions, and d) 026 detecting alignment with said 210 calibration positions by matching said selected arrangements of 014 points with said arrangements of 014 points stored at said 210 calibration positions, such that when said 026 detected alignment occurs, said absolute displacement of said 200 moving part is said known absolute displacement of said 210 calibration position, whereby said estimated absolute displacement of said 200 moving part is corrected at said 210 calibration positions with said stored selected arrangements and estimated between said 210 calibration positions with said stored selected arrangements, and whereby applied markings are not required on said 208 surface of said 200 moving part of said mechanical apparatus under observation.
 14. The optical method of claim 13, further including the steps of: a) detecting an absence of sufficient locations of said 210 calibration positions with said stored selected arrangements of 014 points for sufficient accuracy of said estimating absolute displacement, b) obtaining said absolute displacement of said 200 moving part by an alternate means, and c) storing selected arrangements of 014 points at locations of said 210 calibration positions by an alternate means of obtaining said absolute displacement, such that locations of said 210 calibration positions with said stored selected arrangements are added and said estimated absolute displacement is improved accordingly, whereby said storing selected arrangements of 014 points at locations of said obtained absolute displacements to create new said 210 calibration positions with said stored selected arrangements continues until they are sufficient for alignment of means of said 230 optically capturing said 001 images over said 208 surface of said 200 moving part, and whereby new said 210 calibration positions with said stored selected arrangements are added, replacing any lost or obscured 210 calibration positions with said stored selected arrangements of 014 points.
 15. The optical method of claim 13, wherein the method of said capturing 001 images combines 001 images to form combined 001 image 212 groups, such that when said 001 images are combined to form 212 groups, the complexity of said selecting arrangements of 014 points is reduced, whereby said reduced complexity of said selecting arrangements of 014 points enable faster selection of 014 points, which enables faster movement of said mechanical parts that move with respect to each other.
 16. The optical method of claim 13, wherein the method of said capturing 001 images combines sequences of equally separated 001 images to form combined 001 image 212 groups, such that when said 001 images are combined to form 212 groups, the complexity of said selecting arrangements of 014 points is reduced, whereby said reduced complexity of said selecting arrangements of 014 points enable faster selection of 014 points, which enables faster movement of said mechanical parts that move with respect to each other.
 17. The optical method of claim 14, wherein the method of obtaining by an alternate means of said absolute displacement of said 200 moving part is another said optical method of measuring absolute mechanical displacement of actuators, joints, or other mechanical apparatus that contain mechanical parts that move with respect to each other, whereby multiple said optical methods of measuring absolute mechanical displacement of actuators, joints, or other mechanical apparatus are able to provide alternate means of obtaining said absolute displacement.
 18. The optical method of claim 12, wherein said means of said 230 optically capturing images consists of one or more 925 optical distance sensors, and wherein the method of obtaining known absolute displacement of said 200 moving part, comprising the steps of: a) calibrating one or more said 925 optical distance sensors at said 210 calibration positions, and b) measuring absolute displacement by means of one or more said 925 optical distance sensors, whereby said 925 optical distance sensor measurement of said absolute displacement is verified and 925 optical distance systematic measurement errors are correctable by calibration.
 19. The optical method of claim 13, further including the steps of: a) estimating absolute displacement by means of one or more 925 optical distance sensors, and b) selecting said 210 calibration positions with said arrangements of known absolute positions in the locality of said estimated absolute displacement, whereby the number of said 210 calibration positions that need examination to find a match is greatly reduced by said 925 optical distance sensors, whereby the computational effort required by said means of 026 detecting alignment selected arrangements of 014 points at said 210 calibration positions with said stored selected arrangements is reduced.
 20. The optical method of claim 13, further including the steps of: a) measuring absolute displacement of said 200 moving part with respect to means of said 230 optically capturing 001 images, such that when said 026 detected alignment occurs between selected arrangements of 014 points from said 001 captured images and said arrangements of 014 points stored at said 210 calibration positions, said measuring absolute displacement of said 200 moving part is compared with said known absolute displacement of said 210 calibration position, b) identifying said 210 calibration positions where said measuring absolute displacement of said 200 moving part is in proximity with said known absolute displacement of said 210 calibration position, such that said known absolute displacement of identified said 210 calibration position can be updated with said measuring absolute displacement of said 200 moving part, and c) identifying said 210 calibration positions where said measuring absolute displacement of said 200 moving part is not in proximity with said known absolute displacement of said 210 calibration position, such that identified said 210 calibration position can be deleted, whereby said measured absolute displacement is used to verify said obtained known absolute displacement of said 210 calibration positions, whereby said measured absolute displacement can be used to improve the accuracy of said known absolute displacement of said 210 calibration positions, whereby said measured absolute displacement can be used to identify and delete said 210 calibration positions that are no longer detectable within proximity of their original location, whereby memory used by said 210 calibration positions that are deleted can be released.
 21. The optical method of claim 13, further including the step of selecting said arrangements of 014 points that are globally unique, such that each globally unique said arrangement of 014 points is unique among all said arrangements of 014 points stored at said 210 calibration positions, whereby each said 210 calibration position is identifiable by its globally unique said arrangements of 014 points stored at said 210 calibration positions.
 22. The optical method of claim 13, further including the step of selecting said arrangement of 014 points that are locally unique, such that each locally unique said arrangement of 014 points is unique within the estimating error of said estimated absolute displacement, whereby each selected locally unique said arrangement of 014 points can be very simple and only needs to be unique within the relatively small area defined by said estimating error of said estimated absolute displacement, and whereby each selected locally unique said arrangement of 014 points is simple requiring less 233 non-volatile memory, thus enabling more locally unique said arrangements of 014 points to be stored.
 23. The optical method of claim 12, wherein said 210 calibration positions are adjacent or overlapping, such that said measured relative displacement does not accumulate while moving between said 210 calibration positions, whereby errors in said measured relative displacement do not accumulate in said estimated absolute displacement.
 24. The optical method of claim 12, further including a step of creating marks on said 208 surface of said 200 moving part at said known absolute displacements of said 210 calibration positions, such that series of said created marks form encoded sequences, whereby creating marks on said 208 surface of said 200 moving part allows said 210 calibration positions with said encoded sequences to require significantly less 233 non-volatile memory, whereby creating marks on said 208 surface of said 200 moving part allows said 210 calibration positions to be located sufficiently close to provide an acceptable estimated absolute displacement error, and whereby creating marks on said 208 surface of said 200 moving part allows said 210 calibration positions to be sparsely located to minimize manufacturing costs.
 25. The optical method of claim 13, wherein means of said 230 optically capturing images comprises steps of: a) capturing a plurality of said 001 images from multiple areas of said 208 surface of said 200 moving part, and b) combining said plurality of said 001 images to create a 820 compound image combining optical features from said plurality of said captured 001 images, whereby said 820 compound image combining optical features from said plurality of said captured 001 images has an increased probability of containing unique optical features and as result multiple said 820 compound images are not required to uniquely define said 210 calibration positions.
 26. The optical method of claim 13, wherein said steps of: a) selecting said arrangements of 014 points involves selecting naturally occurring said 014 points that contrast with adjacent naturally occurring surroundings from said 001 images, and b) selecting said arrangements of 014 points stored at said 210 calibration positions involves selecting naturally occurring said 014 points that contrast with adjacent naturally occurring surroundings, whereby a manufacturing process for creating marks on said 208 surface of said 200 moving part is not required, which reduces manufacturing cost. 